The understanding and characterization of changes associated with myocardial ischemia have tremendous clinical importance. In recent years, with the development of multiple clinical methods of intervention and potential for preserving and salvaging areas of ischemia, the development of associated tests for the assessment of changes associated with acute myocardial ischemia becomes of increasing importance. Nuclear magnetic resonance has in the past provided an important method for the in vitro analysis of phosphate and hydrogen metabolites in relation to changes associated with acute ischemia. NMR technology has advanced to a point that in vivo measurements of both hydrogen and phosphorus metabolites can be obtained. We have recently developed and implemented a method for in vivo noninvasive spectroscopy of the myocardium. This technique utilizes a large bore (1 meter) clinical imaging/spectroscopy system and is capable of localizing 31-phosphorus and 1-hydrogen spectra to regions of the myocardium. The goals of this project are to: 1) sensitively characterize these methods in a sequence of phantoms and mathematical models; 2) evaluate the in vivo changes in a series of animals with acute myocardial ischemia over a period of time; 3) assess the effect of reperfusion of an acute ischemia model and to noninvasively separate reversible from irreversible ischemic changes in vivo. A reperfusion model with relatively brief periods of occlusion has been chosen as a model which will represent a relatively large portion of "reversible" ischemia. It is hoped through this systematic evaluation, including phantoms, acute models, and reperfusion, that a sensitive, reliable method for the assessment of acute ischemia can be developed and well characterized so that these methods may be applied to the improved investigation and management of patients with acute myocardial ischemia.